This is a double-blind, randomized, placebo-controlled, multicenter clinical trial to evaluate the safety and efficacy of SP-303 for the treatment of AIDS associated diarrhea. The study design calls for the randomization of approximately 80 patients evaluable for efficacy in each of 4 treatment arms. After an initial inpatient treatment phase, responders will remain on their assigned treatment for an outpatient treatment phase (except patients treated with 500 mg delayed release beads who will be switched to 500 mg delayed release tablets for the outpatient treatment phase). Non-responders will be discontinued from treatment and discharged from the study. All patients will be evaluated for both safety and efficacy in an intent-to-treat analysis.